Method of making molded pulp articles



May 30, 1961 w. H. RANDALL ETAL 2,986,490

METHOD OF MAKING MOLDED PULP ARTICLES Original Filed Oct. 15, 195] 5Sheets-Sheet l INVENTORS WALTER H. RANDALL By a- RICHARD L.EMERYATTORNEYS May 30, 1961 w. H. RANDALL ET AL 2,986,490

METHOD OF MAKING MOLDED PULP ARTICLES Original Filed Oct. 15, 1951 5Sheets-Sheet 2 INVENTORS: WALTER H. RANDALL By a RICHARD 1.. EMERY ATTORNEYS May 30, 1961 w. H. RANDALL ETAL 2,986,490

METHOD OF MAKING MOLDED PULP ARTICLES 5 Sheets-Sheet 3 Original FiledOct. 15, 195] INVENTORS WALTER H. RANDALL 8 RICHARD L. EMERY ATTORNEYS y1961 w. H. RANDALL ETAL 2,986,490

METHOD OF MAKING MOLDED PULP ARTICLES Original Filed Oct. 15, 1951 5Sheets-Sheet 4 .I i J05 Illlllllllllllllllllllllllllll! J06 INVENTORSWALTER H. RANDALL G RICHARD L. EMERY A TTORNEYS y 1961 w. H. RANDALL ETAL 2,986,490

METHOD OF MAKING MOLDED PULP ARTICLES Original Filed Oct. 15, 195] 5Sheets-Sheet 5 8 g N N g E Q 5 *1 1 i"? llllllllllllllllllllllll i l I AINVENTORS: WALTER H. RANDALL RICHARD L. EMERY ATTORNEYS United StatesPatent METHOD OF MAKING MOLDED PULP ARTICLES Walter H. Randall andRichard L. Emery, Waterville, Maine, assignors to Keyes Fibre Company,Portland, Maine, a corporation of Maine Original application Oct. 15,1951, Ser. No. 251,411,

now Patent No. 2,752,830, dated July 3, 1956. Divided and thisapplication Oct. 7, 1955, Ser. No. 539,097

6 Claims. (Cl. 162222) This invention relates to the pressing andfinishing of molded pulp articles after they have been formed tosubstantially the desired shape.

When molded pulp articles are formed they contain a relatively largeamount of water which must be removed. ,In the past this water has beenremoved by subjecting the wet articles to several types of dryingoperations. In one of these, the freshly molded wet article is pressedbetween heated dies corresponding in shape to those with which thearticles are formed. This calls for the use of a relatively large numberof expensive dies. Many types of articles, and particularly those whosedimensions or shapes are not critical, can be dried without the use ofaccurately shaped heating dies, as for example by merely passing them infreely supported condition on a conveyor belt through a steam heateddrying tunnel. This so called free-drying technique is much lessexpensive than chine.

drying them between carefully machined heated dies. I

However, free drying results in at least a small amount of warpage, andthe final article has a somewhat fluify and rough surface appearance.Such an article is often unacceptable to the trade because of the crudeappearance and shape. This is particularly true if such an article is tobe sold or used on the basis of its better appearance.

Among the objects of'the present invention is the provision of improveddrying or finishing methods for the treatment of molded pulp articles togive them the dimensional accuracy and/or degree of surface finish thatis desired. i The above, as well as further objects of the invention,will be more readily understood from the following description ofseveral of its exemplifications, reference being made to theaccompanying drawings wherein; v

Fig. 1 is an elevation, with parts in section, of a drying and finishingapparatus suitable for use in the present invention; H g

' Fig. 2 is a plan view, with parts in section, of the apparatus of Fig.1; 1

Figs. 3 to 7, inclusive, are detail views illustrating a sequence ofoperational. steps involved in the operation of the apparatus of Figs. 1and 2; and

Fig. 8 is an elevational view showing the transfer mechanism portionof.the apparatus of Figs. 1 and 2. According to a preferred embodimentof the present invention, wet molded articles are partially free-dried,and while they still contain an appreciable moisture content, aresubjected to a drying and finishing operation between a set ofcomplemental heated pressing dies. A suitable pressing apparatus forthis purpose includes a series'of mating pairs of complemental dies, oneor both of which may be heated, the series being disposed in an endlessor circular path, driving structure is connected to move the seriesaround this path so that all the individual pairs of mating dies movesuccessively through a predetermined position, operating mechanism isprovided to move one of the dies of each pair away from face appearance.

and into face-to-face relation with respect to the other in a fixedtransfer zone of the travel path, the other die of each pair beingnon-retractably, or substantially nonretractably mounted, said operatingmechanism including loading elements interconnected for delivering anarticle to be dried and finished to one of the dies of each pair whilethese dies are held apart after which the dies are brought intoface-toface relation, pressing means is connected to press the dies ofeach pair together as they leave the transfer zone and to hold themtogether under heat and pressure through a pressing zone that occupiessubstantially the remainder of the travel path, said operating mechanismalso including unloading structure connected for receiving a finishedarticle from the open dies in the transfer zone to remove this articlefrom the apparatus and make way for the next article to be finished. Formaximum efficiency the transfer zone should extend over a minimum amountof the travel path along which the dies progress.

The individual sets of dies can be arranged either to move around thetravel path in short steps or continuously without stopping except whenthe equipment is shut down. The molded pulp articles fed to the machinecan have a moisture content varying from about 10% to 75% or more basedon the total wet weight. After finishing in the above apparatus themoisture content is generally between about 5% and 8%. Where itis desired to obtain a particularly smooth and even glossy finish on themolded article, the moisture content should be preferably at least about25% when it enters the ma The lower initial moisture contents are veryeifectively used when the articles are to be given a lighter finishingtreatment, as for example to iron out any warpage and restore thearticle to substantially its original molded shape with a minimumimprovement of its sur- Below 10% moisture, however, it becomescommercially impractical to-efiect much ironing or surface improvementwithout destroying many of the physical characteristics desired in thefinished article. 7

The drying and finishing apparatus of Figs. 1 to 8, inclusive has a maintable or framework 20 which is journalled on a vertical shaft 22 andcarries a set of radially disposed die holders 24. Each die holder isgenerally C-shaped and includes an upper socket 26 and a lower guide 28or tubular form vertically aligned with each other. The upper sockets 26resiliently hold indi vidual die carriers 30 to which upper dies 32(Fig. 3) are securely fastened. In the form shown the resilient mountingis provided by coil springs 34 seated against the blind upper end ofsocket 26 and holding carrier 30 somewhat below the highest or fullyseated position. The resilience not only acts as a control of the dieclamping force but provides a margin of safety should two or morearticles become accidentally loaded on a single die at the same time.

Vertically slidable in the lower guides 28 are elongated shanks 44 towhich are fastened lower die carriers 40 carrying lower dies 42 (Fig.3). The outer portions of each C-shaped holder 24 also carries, as bymeans of oppositely projecting horizontal pins 46, an opposed pair ofpivoted compression links 48. Suitably :disposed between each pair oflinks is a wedging roller 50 jour nalled about a horizontal axis andengageable with a cut away wedge surface 52 at the lower portion ofshank 44. The shanks also carry independent lifting rollers 54 whichrest upon and cooperate with radially disposed dies. Y

In the above construction the framework 20 is rotated by means ofelectric motor 58 and an internal Geneva movement including a pluralityof circular locking sectors '60 and bars 62 defining radial drivingslots 63 fixed to the cage, along with a rotatable Geneva driver havinga cooperating annular locking segment 64 concentric with segments 60,and driving roller 66 driven by shaft 68. The rotating drive is arrangedso that there is one stepping position or circular sector 60 for eachdie holder 24 and with each revolution of shaft 68, the framework isstepped a distance which brings each holder 24 to the positionpreviously occupied by an adjacent holder. In other words, the stepwiserotation carries each die holder through the same fixed andpredetermined stopping positions between steps. For actuating thecompression links 48, fixed cam operators 70,. 72 are suitably supportedto engage with a cam-following roller 73 fastened on each pair of thelinks. Cam 70 (Fig. 2') is positioned at the end of a pressing zone andhas an inwardly offset portion 74 to effect unlocking of the pressingdies, While cam 72 is located at the beginning of the pressing zone andcauses the dies to be locked in pressed engagement.

In the shorter or transfer zone between the cam operators 70, 72, thedies carried by the holders are arranged to be opened, unloaded, andhave fresh articles supplied, for drying and finishing through thebalance of the table rotation. To effect these transfers, a transferunit 100, shown more clearly in Fig. 8, is mounted alongside theframework 20 in the transfer zone. Unit 100 includes a hollow shaft 102journaled in fixed bearings 104 and carrying a drive gear 106 meshingwith a peripheral ring gear 76 provided on framework 20. Verticallyslidable within hollow shaft 102 and also rotatable alongwith thisshaft,.as by splined interconnection, is a post 108 which carries a pairof oppositely directed unloading dies 110, 111 and another pair ofoppositely directed loading dies 112, 113 (Fig. 2). The lowerend of.post 108 is supported by a rocker lever 114 having a post-engagingblock 116 and pivoted at 118 for actuation by a cam wheel 120. This camwheel in turn is rotated by means of bevel gears 122 (Fig. 1) so as tobe synchronized with the rotation of the main frame 20.

Below the outwardly projecting loading die 113 at position N (Fig. 2)there may be positioned a supply unit 200 for feeding individual moldedarticles to be pressed. Although the form of this unit is not criticalto the present invention, US. Patent No. 2,752,830 describes a preferredembodiment thereof.

For simplifying the transfer of the articles being treated from one dieto another, the dies may be perforated and fitted with suction and/orcompressed air supplies. Control units 80 (Fig. l) operated as by cams82 driven in synchronism with the transfer unit 100 provide the desiredtiming of these transfer assisting features. Connections such as sliprings 86 are provided to conduct heating current to the pressing dies32, '42 on the main frame 20. In addition a rotary valve assembly 87 canbe arranged to establish vacuum and/or compressed air connections tothese dies for operation at desired portions of the rotation cycle.

Referring more particularly to Fig. 2, as the frame 20 rotates, a pairof pressing dies is moved into position A while the loading transferdies 112, 113 are rotated around to interchanged position and verticallyreciprocated. At position A after the completion of the advancing step,the parts are then in the relationship shown in Fig. 3. During thevertical reciprocation one loading die 113 is brought against the top ofthe stacked plates in supply unit 200.

While this loading is taking place, the opposite loading die 112 isbrought down against the open pressing die 42 just below it, as shown inFig. 4 and deposits a previously loaded plate-on this die. Suction cannow be cut off from the loading die, applied to the pressing die and/ora puff of compressed air used to help this deposition.

The final lifting of the loading dies at the completion of the verticaloscillation returns the loading die 112 to the position shown at Fig. 3.

The next step in the rotation of frame 20 carries the open pressing dieswith the transferred plate from position A to position B. Cam segment 56here lifts the lower die 42 with its plate up against the upper die 32as shown in Fig. 5. At the same time or shortly thereafter cam 72carries the pressing link 48 outwardly to the positions shownconsecutively in Figs. 5, 6 and 7.- At the position of Fig. 6 thewedging roller 50 is brought into engagement with the wedge surface 52and the upper die 32 has not yet been forcefully engaged so that it maystill be suspended by its resilient mounting.

Continued movement of link 48 to the position of Fig. 7 causes the lower,die to be wedged upwardly by roller 50, compressing the resilientsupport for the upper dieand applying the desired pressing to the loadedplate.

At about this time heat may be applied to the dies, as by closing anelectric circuit to electric heaters in both dies 32, 42. Alternativelythe heating can be maintained uninterruptedly throughout the rotation ofthe main frame. From position B the closed dies are kept locked by thepressing links and are then stepped through positions C, D, E, F, G, H,J, K without interrupting the pressing. The locking of the compressinglinks can be secured by providing these links 48 with an over-centerholding arrangement as by suitably shaping the wedging surface 52 in themanner shown in the figures.

Upon the movement of the dies through the steps L and M the links 48 arefirst unlocked by cam operator 70 and the lower die permitted to drop bythe suitably shaped upper surface of cam segment 57. The diesaccordingly open by retracing the sequence through the positions shownat Figs. 7, 6, 5 and 3. However, at position M, the open pressing dieshave between them one of the unloading dies 110 instead of the loadingdie 112 shown in Fig. 3.

When the dies reach position M, or as they are about to move from thereto position A, the vertical reciprocation of the transfer shaft 108carries the unloading die 110 against the lower die 42 just beneath itas in Fig. 4, and with or without the assistance of suitably directedsuction and/or compressed air, the plate that has been through thepressing cycle is transferred to this unloading die. Upon rotation ofthe transfer shaft 108 this unloading die is moved to position P (Fig.2) where it then blows or permits the unloaded plate to drop onto asuitable discharge receptacle or conveyor, not shown.

This unloading sequence of the transfer mechanism, as

- 7 described above, can be effected at the same time as the loading. Inother words, each step of the transfer unit corresponding to a step ofthe main frame 20 can include a single vertical reciprocating step whichsimultaneously does the following operations:

It will thus be seen that the stepping of the pressing dies fromposition M toposition A is accompanied by the unloading of thepreviously pressed plate and the loading of a fresh plate. From positionA the dies then repeat the cycle described above so that the plates arecontinuously being loaded, pressed and discharged.

The pressingdies of the apparatuses of Figs. 1-8 are preferably heatedto between about 250 and 450 F.

Lower die temperatures can also be used but require longer pressingtreatments to effect the desired drying.

As many apparently widely different embodiments of the invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that the invention is not limited to the specific embodimentsthereof except as limited by the appended claims. Thus the transferdevice of the construction of Fig. 2 can be used to feed to and unloadarticles from other article handling devices such as printers,labellers, etc.

This application is a divisional application of application Serial No.251,411 of October 15, 1951, now U.S. Patent No. 2,752,830 of July 3,1956.

What is claimed is:

1. In a method of molding pulp articles, including the steps ofimmersing into a liquid pulp slurry a foraminous mold under suction todeposit a layer of wet pulp thereon which initially forms a molded pulparticle, and removing the mold from the slurry; the improvements whichcomprise free drying the wet pulp article without compression to effectonly partial removal of the moisture therein while retaining sufiicientmoisture in the article to permit substantial smoothing of the surfacesthereof upon the application of heat and pressure, and then subjectingthe partially dried article to compression between heated dies to removethe remaining moisture and impart a smooth surface finish to thearticle.

2. A method of finishing wet molded pulp articles, which methodcomprises free drying the wet molded articles to a moisture content ofabout 25 to about 75% based on the total wet weight, and completing thedrying by pressing between heated dies having pressing surfaces shapedto provide the desired finish.

3. A method of finishing wet molded pulp articles, which methodcomprises free drying the wet molded articles to a moisture content ofabout to 75 based on the total wet weight, and completing the drying bypressing between heated dies having pressing surfaces shaped to providethe desired finish.

4. In a method of molding pulp articles, including the steps ofimmersing into a liquid pulp slurry a for-aminous mold under suction todeposit a layer of wet pulp thereon which initially forms a molded pulparticle, and removing the mold from the slurry; the improvements whichcomprise free drying the wet pulp article without compression to amoisture content of about 10 to about based on the total wet weight andthen subjecting the partially dried article to compression betweenheated dies to remove the remaining moisture and impart a smooth surfacefinish to the article.

5. The method of claim 4 wherein the wet pulp article is free driedwithout compression to a moisture content of about 25 to about 75% basedon the total wet weight.

6. A method for pressing partially free-dried molded pulp articlescontaining a moisture content from about 10 to 75 based on their totalwet weight, said method including the steps of continuously moving aseries of pressing die sets along a predetermined feed path, each setcomprising a pair of complementary dies and said dies being maintainedin spaced, open relation to each other during their movement along saidfeed path, supplying individual articles to be molded and sliding themsuccessively to the dies as they move in open relation, closing themoving dies on the successively fed articles, to press them for thedesired time, opening the moving dies after the pressing, andindividually removing the pressed articles from the open dies whilemaintaining the movement of said dies.

References Cited in the file of this patent UNITED STATES PATENTS759,616 Keyes May 10, 1904 1,618,289 Koppelman Feb. 22, 1927 2,046,750Mason et al. July 7, 1936 2,080,077 Howard et al. May 11, 1937 2,234,979Randall et al. Mar. 18, 1941 2,309,206 Newman Jan. 26, 1943 2,369,488Perry Feb. 13, 1945 2,388,828 Chaplin Nov. 13, 1945 2,704,493 RandallMar. 22, 1955

4. IN A METHOD OF MOLDING PULP ARTICLES, INCLUDING THE STEPS OFIMMERSING INTO A LIQUID PULP SLURRY A FORAMINOUS MOLD UNDER SUCTION TODEPOSIT A LAYER OF WET PULP THEREON WHICH INITIALLY FORMS A MOLDED PULPARTICLE, AND REMOVING THE MOLD FROM THE SLURRY, THE IMPROVEMENTS WHICHCOMPRISE FREE DRYING THE WET PULP ARTICLE WITHOUT COMPRESSION TO AMOISTURE CONTENT OF ABOUT 10 TO ABOUT 75% BASED ON THE TOTAL WET WEIGHTAND THEN SUBJECTING THE PARTIALLY DRIED ARTICLE TO COMPRESSION BETWEENHEATED DIES TO REMOVE THE REMAINING MOISTURE AND IMPART A SMOOTH SURFACEFINISH TO THE ARTICLE.